This invention relates to apparatuses for detecting the beginnings of data words into digital data transmission, such as between individual apparatuses of an avionics system and particularly to devices which may be called digital word start detectors, interword space detectors, stop code detectors, start code detectors, or GAP detectors.
Such detectors may be composed of two switching branches which define a trigger pulse for the beginning of a data word by comparing the output signals of the branches.
Such detectors operate with signals that may be designated interword spacer pulses, or start and stop code pulses. These pulses serve to time separate the individual signals proper at a data receiver. The data transmission between individual apparatuses of an avionics system is effected primarily by means of serial digital signals. Up to 32 signals can be transmitted successively on one data channel. This transmission takes place periodically and in the order of the signals 1, 2, 3,...32 etc. Each signal is composed of a 26 bit data word. Apart from the 16 bit signal proper, the word contains a number of recognition and test pulses and six so-called stop code or start code pulses (GAP pulses) at the end or beginning of each data word. The stop code or start code pulses signal the end of a word of the beginning of a new word.
Heretofore, known detectors counted the bits of the data word and depended on the length of the data word. The disadvantage of such known devices is that the apparatus is not suitable for changes or can be adapted for changes only with great difficulty.
Other known detectors of the above-mentioned type use monoflops. However, these embodiments depend upon the clock frequency and must therefore be specially calibrated.
An object of the invention is to improve the aforementioned devices.
Another object of the invention is to produce a pulse code detector which is independent of the clock frequency and the length of the data word. The term "stop code pulses" is used for simplicity to define the signals which separate the words.